(1) Field of the Invention
This invention relates to a coating method and a coating apparatus for applying a coating solution, e.g. an SOG (Spin On Glass) solution (also called silica film forming material), a resist sensitizing agent or a polyimide resin to semiconductor wafers, glass substrates for photomasks, glass substrates for liquid crystal displays or substrates for optical disks (hereinafter called simply the substrates). More particularly, the invention relates to a technique for forming a film of the coating solution on a substrate with high accuracy.
(2) Description of the Related Art
Conventionally, what is called the spin coat method is used as this type of method. The spin coat method is a method of forming a thin film of the coating solution on a substrate by supplying the coating solution to a central region of the substrate, and spinning the substrate at high speed to apply centrifugal force to the coating solution and spread the coating solution to edges of the substrate. When the coating solution is spread, an excess part of the coating solution supplied to the substrate is spun off the substrate to be discarded. This constitutes a bad use efficiency of the coating solution, resulting in large consumption of the coating solution.
Besides the spin coat method, there is a method based on an inkjet mode. This method forms a film on a substrate by discharging minute droplets of the coating solution from nozzles of an inkjet head uniformly over the substrate. This method, which is capable of forming a film without spinning the substrate to apply and spread the coating solution, can reduce consumption of the coating solution (as disclosed in Japanese Unexamined Patent Publication No. 2002-66391, for example).
However, the conventional example with such construction has the following problem.
The inkjet mode, since a film is formed of an aggregation of droplets, has a disadvantage that it is difficult to smooth the surface of the film.